This work compares the physicochemical properties and fatty acid (FA) compositions of waste cooking oil (WCO) collected after deep frying periods from local restaurant with samples of refined cooking oil (RCO) produced after degumming, alkaline and bleaching treatments. The refined oil were initially kept/stored in the refrigerator at 4 o C and the biodiesel produced was subjected to gas chromatography mass spectroscopy (GCMS) for FA profile, and to Fourier Transform Infrared (FTIR) analyses to monitor esterification reactions. The degree of oil usage affected WCO properties and fatty acid composition. Density of refined cooking oil RCO and WCO varied between 0.90 and 0.93 (g/cm 3 ), and of refined cooking methyl ester (RCME) and waste cooking methyl ester (WCME) between 0.88 and 0.91 (g/cm 3 ). The pH of RCO and WCO varied between 7.36 and 8.61 and that of RCME and WCME between 5.11 and 5.59. The results of RCO and RCME showed corresponding improvements over the WCO and WCME in recovery yield, acid value, saponification value, iodine value, peroxide value, cetane number, kinematic viscosity, pour, smoke, flash, and fire points. Fatty acids analyses similarly showed comparable differences between the RCO and WCO with percent increase in octanoic ethyl acid (276.54%), benzoic acid, butyl ester (69.79%), hexadecanoic acid 15-methyl esters (267.33%) and reduction in 9,17-Octadecanoic acid (99.20%), and 9-octadecenoic acid(35.98%), respectively. The hexadecanoic acid, methyl ester (54.10%) was the most abundant. This result confirms the suitableness of WCO as feedstock for biodiesel.

The effects of designed protection conditions such as different antioxidants (propyl gallate, PG and Pyrogallol, PY), antioxidant concentration (30 – 600 ppm), temperature (30˚C -120˚C) and storage period (3 – 5 days) on the oxidation stability of castor biodiesel were investigated work was to assess the effect of the antioxidants on the oxidative stability of castor biodiesel. Using the American Standard for Testing Materials (ASTM) recommended protocols to determine the changes in the physicochemical properties (acid value, p-anisidine value, peroxide value, totox value, density, kinematic viscosity and refractive index) of the castor biodiesel were measured. The protection conditions were optimized using the Response Surface Methodology (RSM) according to the Box–Behnken Design (Design Expert version 11 Statistical Software). The analysis of variance (ANOVA) of propyl gallate showed concentration levels and temperature as the most important factors in the biodiesel oxidation, whereas the day of storage was one of the lowest factors with the p-value of < 0.05 for most indicated process variables of both linear and quadratic model terms were significant. The changes in some important physicochemical values are indication of degradation occurring in the biodiesel under the set storage condition. The optimal storage conditions were observed in propygallol with the acid value (0.985 mg KOH/g), p-anisidine value (7.650 mg KOH/g) and Totox value 4.005 (mEq/kg) with the overall desirability of 0.923 based on comparatively lower acid, p-anisidine and Totox values, followed by PG. The combined use of PY/PG antioxidants didn't show a synergic or additive result that makes the mixture of those antioxidants unsuitable to boost the biodiesel stability based on their relatively higher Totox Value.